Now that you’ve taken part in Sky Day, let’s make use of your sky photos to learn more about our Earth’s atmosphere and climate system. If you haven’t taken a photo of the sky yet, that’s ok! Get outside and take one now. The following lessons and activities focus on those white puffy beauties likely present in most of your Sky Day photos – that’s right, clouds! You’ll learn about the science behind cloud formation and how to identify cloud types. You’ll also have the opportunity to take part in a creative writing project and to share your story with others all across the globe. We challenge you to get inspired by the beauty and dynamic nature of our sky!

Lesson 1: Cloud Formation

Let’s get started with some cloud FAQs.

What are clouds made of? H2O! Clouds are composed of water droplets or ice crystals. Clouds are a very important part of the water cycle!

Where in Earth’s atmosphere do clouds form? Although the sky seems endless, Earth’s atmosphere is relatively thin. Atmospheric scientists have divided the atmosphere into several layers according to the height above Earth’s surface. Most clouds lie within the first zone, named the troposphere. It extends from the Earth’s surface to up to about 20 km. As you may have guessed, this layer is where almost all weather occurs. If you would like to learn more about the troposphere or the other layers of Earth’s atmosphere, check out this NOAA webpage.

Fun fact! The height of the tropopause (where the troposphere ends and the stratosphere begins) is not the same in all places. In fact, its height varies by latitude. At the poles, it’s just about 6.5 km high, but at the equator extends up to ~ 20 km.

How do clouds form? Let’s think about clouds like your favorite recipe. To make a cloud you need three main ingredients: moisture (water vapor), cooling air (a reduction in pressure), and condensation nuclei (we’ll explain this one more in a minute). As warm air rises, pressure is reduced, causing the air to expand and cool. When the temperature drops below the dew point, or enough for water vapor to condense, water molecules attach themselves to particles in the air, such as dust, smoke, or other aerosols (these are the nuclei!). As more molecules of water vapor condense into water droplets on the nuclei, a visible cloud forms!

Why does it rain? Most clouds are composed of water droplets that are so tiny and light that they are able to float in the air. But, as the water droplets combine with one another, they form larger droplets and become heavier. Eventually, gravity causes the droplets to fall to Earth’s surface – rain! When it’s really cold outside, snow, sleet, or hail falls instead.

Why do scientists study clouds? Clouds are very important to Earth’s water cycle, and its weather and climate system! Scientists study clouds to better understand these systems. Many scientists use space-based instruments called satellites to monitor clouds. To see some really cool cloud images taken by NASA satellites, visit this webpage.

And, for more background information on clouds, visit this webpage.

Activity 1: Cloud in a bottle Experiment  

Now that you know the basics of cloud formation, you can create your own!

What you’ll need: A flexible 2-liter clear plastic bottle, matches (make sure to ask for an adult’s help!), and some warm water.

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Procedure:

Step 1: Fill your plastic bottle about 1/3rd full of warm water, then place the cap back on tightly. The warm water inside will start to evaporate, making the air above full of water vapor (don’t worry if you don’t see anything happening -- water vapor is a gas and is not visible to our eyes). If the sides of the bottle become covered in water droplets, shake the bottle so you can see clearly through the plastic again.

Step 2: Remove the cap from the bottle. Ask an adult to light a match, let it burn for 2 seconds, and then drop it into the bottle. After the match is inside, quickly put the cap back on!

Step 3: Squeeze and release the bottle until a cloud appears! When the cloud has formed, quickly unscrew the cap and let the cloud escape from the bottle.

So, what’s happening? Let’s go back to our three cloud making ingredients -- water vapor, a pressure reduction, and condensation nuclei. Adding warm water to the bottle allows the air above to become filled with water vapor. Adding the match to the bottle produces plenty of nuclei (smoke) for the water vapor to condense onto. And finally, squeezing and then releasing the bottle causes a reduction in pressure and the air in the bottle to cool and condense into water droplets, forming your cloud!

Quick tips! On your next trial, try adding a little food coloring to the water, this may help you see your cloud better. If you still have trouble seeing your cloud, try shinning a flash light into the bottle, or place a black piece of paper behind the bottle.

Think about it! Why was the smoke needed for the cloud to form? And, why did you need to squeeze and release the bottle for the cloud to form?

 

Lesson 2: Discovering Cloud Types

 

Have you ever looked up at the clouds in the sky and noticed how different they all are? Some look like floating cotton balls and other’s look like wispy cotton candy. Scientists have developed a classification system for clouds based on where they are in Earth’s atmosphere (or their altitude), their shape, and how much precipitation they produce.

 

Do some research on your own or refer to the descriptions below to learn about some cloud types! If you’d like to research on your own, here’s a good place to start! And for a visual guide, visit this NOAA webpage.

 

Shape: Clouds come in many shapes and sizes. The three main cloud shapes include:

  • Heaped and puffy (cumulus clouds)

  • Layered (stratus clouds)

  • Wispy (cirrus clouds)

 

Altitude: Some clouds form low in Earth’s troposphere, while others form higher up.

High clouds are defined as clouds above 6,000 m and are termed with the prefixes "cirrus" or "cirro-“. Examples of high clouds include:

  • Cirrus

  • Cirrocumulus

  • Cirrostratus

Middle clouds are defined as clouds between 2,000 - 6,000 m and are termed with the prefix "alto-". Examples of middle clouds include:

  • Altocumulus

  • Altostratus

Low clouds are defined as clouds below 2,000 m and have no set prefix. Examples of low clouds include:

  • Stratus

  • Nimbostratus

  • Cumulus

  • Stratocumulus

  • Cumulonimbus

  • Fog

Check out NASA’s cloud identification chart below! Can you identify the 12 clouds types?

Image credited to NASA's S'Cool  Globe Learning and Observations to Benefit the Environment

Image credited to NASA's S'Cool  Globe Learning and Observations to Benefit the Environment

Activity 2a: Sky Day Photo Cloud ID

You know so much about clouds! Now it’s time to use that knowledge to identify the clouds in your Sky Day photo. Remember to consider the shape and texture of your cloud, and where it sits in the sky. If you need help, refer to NASA’s cloud checklists.

Note: If you don’t have a photo of the sky with clouds consider trying to identify the clouds in the photos posted on the Only One Sky webpage.

Activity 2b: From a Cloud’s Perspective

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Your cloud is unique and has a story! We challenge you to write a story or poem written from your cloud’s perspective. The story or poem can describe how they came to be a cloud, what type of cloud they are, what it’s like to be a cloud, or what your cloud would see traveling across an area, etc. Be creative and have fun! And, to share your cloud story on the ‘Only One Sky’ webpage, follow these steps.

Step 1: With your teacher’s help, record your cloud story by reading it aloud. Try to keep your story to under 2 minutes or less.

Step 2: Ask you teacher to arrange with Only One Sky for your video to be uploaded.

Your cloud story will be attached to your Sky Day photo on the ‘Only One Sky Kids’ webpage, allowing you to share your story or poem and listen to cloud stories from all over the world. 

Lesson 3: The Role of Clouds in Earth’s Climate System

Clouds interact with Earth’s climate system in many complex ways. Water vapor in the atmosphere (an important ingredient in cloud formation) also acts as a powerful greenhouse gas. Greenhouse gases trap in heat radiating from Earth toward space, warming our planet. You may have heard a lot about Carbon Dioxide, another greenhouse gas, which has been increasing in concentration in recent centuries due to fossil fuel burning, ultimately contributing to anthropogenic climate change.

Water vapor also acts as a climate feedback because the amount of water vapor in the atmosphere is directly related to its temperature. The warmer our atmosphere, the more water vapor it can hold. Since water vapor is a greenhouse gas, additional water vapor in the atmosphere causes the temperature to rise even more. This relationship is called a positive feedback. Thus, water vapor amplifies the effect of CO2 warming.

Now let’s talk about clouds! The more water vapor in the atmosphere, the more clouds! Because clouds are bright white, the tops of clouds reflect most of the incoming sunlight that hits them back into space. However, since clouds also blanket the Earth, they keep some heat from escaping too. The effect of clouds on Earth’s climate system is very complicated and many scientists are working to understand them better. Check out this webpage to learn more about how NASA scientists are using satellites (like Aqua and CloudSat), to study the Earth's water cycle and clouds.

Activity 3: Global Warming in a Jar

To see how the greenhouse effect works, try this experiment!

This educational guide was written by Laura Larocca. Laura is currently a graduate student in the Earth and Planetary sciences Department at Northwestern University. She also has a background in K-5 education and fine arts.